There is today an increasing demand from passengers to be able to communicate through mobile phones and other handheld terminals when travelling on trains, and also to be able to get access to the Internet with laptops, PDAs etc. However, train carriages are made of metal, and even the windows are normally covered with a metal film. Accordingly, train carriages are shielded compartments, and direct communication between terminal antennas within the carriages and externally located antennas is difficult to obtain. Further, with the new smartphones, and the way these are used, with e.g. continuously operating applications, many phones are active at all times, meaning that many handovers are required when the train moves. Even though this problem is common for all moving vehicles, it is especially pronounced for vehicles moving at high speed, such as trains.
To this end, train carriages are often provided with an external antenna connected to a repeater unit within the carriage, which in turn is connected to an internal antenna. Hence, the communication between the passengers' terminals and the operator antennas outside the trains occurs through the repeater unit. Similarly, it is known to provide a mobile access router for data communication, also connected both to an external antenna and an internal antenna, in each carriage, in order to provide Internet access on-board the train. Such mobile access router solutions are e.g. commercially available from the applicant of the present application, Icomera AB, of Gothenburg, Sweden.
However, today's systems are not entirely satisfactory. Trains often pass through areas with bad radio coverage, and the repeater units, nowadays handling both traditional voice communication and data communication, through e.g. 3G, are often unable to handle the required traffic. As a consequence, telephone conversations will often be disrupted and disconnected inadvertently.
Another drawback with today's systems is that there is a frequent need for upgrading of the systems, since the repeater units need to be able to handle all available frequency bands and be up to date with all new system requirements. This means that several units in each carriage frequently need to be replaced, which is a very costly procedure. It is also difficult to supervise the operation of the different components of the system, which leads to cumbersome and costly error detections etc in cases of malfunction. As a consequence, the operation performance is often deteriorated due to problems not being recognized. Malfunctioning repeaters also often deteriorate other communication equipment on-board a train, such as data communication equipment. Further, even properly functioning repeaters may deteriorate the performance of other communication equipment.
Another drawback with today's systems is that the repeater units and the mobile access router require a significant amount of space and power. Consequently, these units need to be placed in a separate cooled compartment on the train. Since both power and space is a scarce resource on-board a train, this significantly adds to the costs of using the known systems.
Still another drawback with today's systems is that is difficult or even impossible to implement new and more efficient transmission solutions, such as MIMO.
In EP 2 665 331 by the same applicant, a wireless train communication system is disclosed using femtocells in the train. Even though this solution has provide to be a very efficient remedy to at least some of the above-discussed general problems, it is still not useable in all situations, and also it requires use of dedicated, licensed frequencies, which are costly and may not always be available. The use of such frequencies in a moving vehicle may also be problematic. Further, this solution often requires that an agreement is reached with all operators, which in practice may be difficult. Still further, even though this known solution provided great cost advantages compared to previous solutions, it is still relatively costly to install and maintain.
There is therefore a need for an improved train communication system which provides better capacity and/or lowers the overall costs of installing and maintaining the system. Even though the above discussion is focused on trains, similar situations and problems are at least to some extent encountered in many other types of moving passenger vehicles, such as buses, ships and airplanes.